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Organosoluble zirconium phosphonate nanocomposites and their supported chiral ruthenium catalysts: The first example of homogenization of inorganic-supported catalyst in asymmetric hydrogenation
In this article, we report the synthesis, structure, morphologies, and asymmetric catalytic properties of a series of novel organosoluble zirconium phosphonate nanocomposites and their supported chiral ruthenium catalysts, which have a good organosolubility (0.1-0.5 g mL-1) in various solvents and mesoporous, filiform, and layered structures. Due to the organosoluble properties in various organic solvents, the first homogenization of zirconium phosphonate-supported catalyst was realized in the field of catalysis. In the asymmetric hydrogenation of substituted α-ketoesters, enantioselectivities (74.3-84.7% ee) and isolated yields (86.7-93.6%) were higher than the corresponding homogeneous Ru(p-cymene)(S-BINAP)Cl2 due to the confinement effect caused by the remaining mesopores in the backbone of the zirconium phosphonate. After completing the reaction, the supported catalyst can be readily recovered in quantitative yield by adding cyclohexane and centrifugation, and reused for five consecutive runs without significant loss in catalytic activity.
Chen, Taotao,Ma, Xuebing,Wang, Xiaojia,Wang, Qiang,Zhou, Jinqin,Tang, Qian
experimental part
p. 3325 - 3335
(2011/05/13)

A Rule To Predict Which Enantiomer of a Secondary Alcohol Reacts Faster in Reactions Catalyzed by Cholesterol Esterase, Lipase from Pseudomonas cepacia, and Lipase from Candida rugosa
The enantioselectivity of the title enzymes for more than 130 esters of secondary alcohols is correlated by a rule based on the sizes of the substituents at the stereocenter.This rule predicts which enantiomer of a racemic secondary alcohol reacts faster for 14 of 15 substrates of cholesterol esterase (CE), 63 of 64 substrates of lipase from Pseudomonas cepacia (PCL), and 51 of 55 cyclic substrates of lipase from Candida rugosa (CRL).The enantioselectivity of CRL for acyclic secondary alcohols is not reliably predicted by this rule.This rule implies that the most efficiently resolved substrates are those having substituents which differ significantly in size.This hypothesis was used to design syntheses of two chiral synthons: esters of (R)-lactic acid and (S)-(-)-4-acetoxy-2-cyclohexen-1-one, 70.As predicted, the acetate group of the methyl ester of lactyl acetate was hydrolyzed by PCL with low enantioselectivity because the two substituents, CH3 and C(O)OCH3, are similar in size.To improve enantioselectivity, the methyl ester was replaced by a t-butyl ester.The acetate group of the tert-butyl ester of lactyl acetate was hydrolyzed with high enantioselecticity (E > 50).Enantiomerically pure (R)-(+)-tert-butyl lactate (>98percent ee, 6.4 g) was prepared by kinetic resolution.For the second example, low enantioselectivity (E 65) using either CE or CRL.Enantiomerically pure 70 (98percent ee) was obtained after removal of the bromines with zinc and oxidation with CrO3/pyridine.
Kazlauskas, Romas J.,Weissfloch, Alexandra N. E.,Rappaport, Aviva T.,Cuccia, Louis A.
p. 2656 - 2665
(2007/10/02)

BIOCATALYTIC RESOLUTION OF (+/-)-HYDROXYALKANOIC ESTERS. A STRATEGY FOR ENHANCING THE ENANTIOMERIC SPECIFICITY OF LIPASE-CATALYZED ESTER HYDROLYSIS.
A general biocatalytic procedure for the preparation of a variety of R- and S-hydroalkanoic esters of high optical purity has been developed.The noteworthy feature of this methodology resides in the selection of a nonhydrolyzable ester at the carboxyl terminus to improve the enantiospecificity in the lipase-catalyzed hydrolysis of the acyloxy ester.
Scilimati, A.,Ngooi, T. K.,Sih, Charles J.
p. 4927 - 4930
(2007/10/02)

Chiral Synthesis via Organoboranes. 15. Selective Reductions. 42. Asymmetric Reduction of Representative Prochiral Ketones with Potassium 9-O-(1,2:5,6-Di-O-isopropylidene-α-D-glucofuranosyl)-9-boratabicyclononane
Potassium 9-O-(1,2:5,6-di-O-isopropylidene-α-D-glucofuranosyl)-9-boratabicyclononane (9-O-DIPGF-9-BBNH, K-glucoride), a new stable chiral borohydride reducing agent, was prepared by reaction of the corresponding borinic ester, 9-O-DIPGF-9-BBN, with potassium hydride in THF.The reagent provides high optical induction for asymmetric reduction of prochiral ketones, such as relatively hindered aliphatic ketones, alkyl aromatic ketones, and α-keto esters.In particular, the reduction of hindered α-keto esters provides the corresponding α-hydroxy esters with optical purities approaching 100percent ee.Moreover, the reduction of relatively hindered aliphatic ketones such as 3,3-dimethyl-2-butanone, 2,2-dimethylcyclopentanone, spirononan-1-one, and 2,2-dimethylcyclohexanone yields the corresponding alcohols in 70percent ee, 84percent ee, 82percent ee, and 64percent ee, respectively.The reduction of unhindered aliphatic ketones such as 2-butanone, 3-methyl-2-butanone, 2-octanone, and cyclohexyl methyl ketone provides the corresponding alcohols in relatively low optical purities, 3percent ee, 39percent ee, 27percent ee, and 23percent ee respectively.Alkyl aromatic ketones are reduced to the corresponding alcohols, providing products in 78percent ee for acetophenone, 92percent ee for propiophenone, 87percent ee for butyrophenone, 87percent ee for isobutyrophenone, 85,4percent ee for valerophenone, 97-100percent ee for pivalophenone, and 91percent ee for 2'-methylacetophenone.The reduction of α-keto esters provides the corresponding α-hydroxy esters in exceptionally high ee, such as 86percent ee for methyl pyruvate, 86percent ee for ethyl pyruvate, 87percent ee for isopropyl pyruvate, 81percent ee for tert-butyl pyruvate, 92percent ee for ethyl 2-oxobutanoate, 94percent ee for ethyl 2-oxopentanoate, 98percent ee for methyl 3-methyl-2-oxobutanoate, 97percent ee for ethyl 3-methyl-2-oxobutanoate, 97percent ee for methyl 3,3-dimethyl-2-oxobutanoate, 98percent ee for ethyl 3,3-dimethyl-2-oxobutanoate, 93percent ee for ethyl 4-methyl-2-oxopenyanoate, 92percent ee for methyl benzoylformate, 94percent ee for ethyl benzoylformate, 93percent ee for isopropyl benzoylformate, and 96percent ee for ethyl α-oxo-1-naphthaleneacetate.The reduction of relatively more hindered ketones such as 3,3-diethyl-2-pentanone, 2,2,2-triphenylacetone, 2,2,2-triethylacetophenone, 2,2,2-triphenylacetophenone, and 2',4',6'-trimethylacetophenone results in a serious decrease in optical purity, 25percent ee, 7percent ee, 34percent ee, 4percent ee, and 35percent ee, respectively. 4-Chlorobenzophenone is reduced to 4-chlorobenzhydrol in only 11,5percent ee.Ethyl 2,2-dimethylacetoacetate is reduced to ethyl 2,2-dimethyl-3-hydroxybutanoate in 43percent ee.The reductions of alkyl heterocyclic ketones such as 2-acetylfuran, 2-acetylthiophene, and 3-acetylpyridine afford the corresponding alcohols with 42percent ee, 42percent ee, and 70percent ee, respectively.The reductions of α-halo ketones, 2-chloroacetophenone and 2,2,2-trifluoroacetophenone, yield the corresponding halohydrins in 77percent ee and 48percent ee, respectively. trans-4-Phenyl-3-buten-2-one is reduced to the corresponding allylic alcohol in 60percent ee.The reduction of 4-phenyl-3-butyn-2-one provides the corresponding acetylenic alcohol in 61percent ee.The ...
Brown, Herbert C.,Cho, Byung Tae,Park, Won Suh
p. 1231 - 1238
(2007/10/02)

STEREOCONTROLLED SYNTHESIS OF D-α-HYDROXY CARBOXYLIC ACIDS FROM L-AMINO ACIDS
Optically active D-α-hydroxy carboxylic acids are obtained from L-amino acids via L-α-halocarboxylic acids and their stereoselective reaction with cesium p-nitrobenzoate.
Kunz, Horst,Lerchen, Hans-Georg
p. 1873 - 1876
(2007/10/02)

Antiglaucoma agents
Pharmaceutical compositions and a method for reducing intraocular pressure by topically applying a carboxyalkyl dipeptide are disclosed.
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(2008/06/13)

Selective Reductions. 37. Asymmetric Reduction of Prochiral Ketones with B-(3-Pinanyl)-9-borabicyclononane
The chiral trialkylborane B-(3-pinanyl)-9-borabicyclononane, either with the neat reagents or concentrated solutions, 2 M, reduces a wide range of prochiral carbonyl compounds with good to excellent asymmetric induction.Reduction of simple dialkyl ketones, 2-butanone, 2-octanone, 3-methyl-2-butanone, and 3,3-dimethyl-2-butanone, yields the corresponding alcohols with 43percent, 48percent, 62percent, and 0.7percent asymmetric induction.Acetophenone is reduced to 1-phenylethanol in 85percent ee.The α,β-unsaturated ketones 3-buten-2-one, 1-acetyl-1-cyclohexene, 3-methyl-2-cyclohexenone, and trans-4-phenyl-3-buten-2-one are reduced to the corresponding allylic alcohols with 57percent, 64percent, 11percent, and 97percent asymmetric induction, respecticvely.The α,β-conjugated acetylenic ketones 3-butyn-2-one, 4-methyl-1-pentyn-3-one, and 4-phenyl-3-butyn-2-one underwent a rapid reduction to afford the corresponding propargylic alcohols with 79percent, 99percent, and 91percent enantiomeric purities.The α-haloalkyl aromatic ketones α-chloroacetophenone, α-bromoacetophenone, α-iodoacetophenone, α,p-dibromoacetophenone, α-bromo-p-cyanoacetophenone,α-bromo-2'-acetonaphthone,and α,α,α-trifluoroacetophenone afforded the corresponding halohydrins with 96percent,93percent,93percent,96percent,96percent,90percent,and35percent enantiomeric purities, respectively.The corresponding aliphatic analogue 1-bromo-3-methyl-butanone gave the halohydrin in 66percent ee.The other isomer of this ketone, 3-bromo-3-methyl-2-butanone, failed to undergo reduction.Both the aliphatic and aromatic α-keto esters underwent rapid reduction to give the corresponding α-hydroxy esters with excellentenantiomeric excesses.Thus, methyl, ethyl, isopropyl, and tert-butyl pyruvates afforded the corresponding lactates with 86percent,83percent,78percent, and 92percent ee at 25 deg C,respectively.Lowering the reaction temperature to 0 deg C gave the tert-butyl lactate in 100percent ee.Other aliphatic α-keto esters such as metyl and ethyl 2-oxopentanoates, methyl 3-methyl-2-oxobutanoate, and ethyl 4-methyl-2-oxopentanoate were reduced to the corresponding α-hydroxy esters with 96percent, 96percent, 11percent, and 82percent ee.The methyl, isopropyl, and tert-butyl benzoylformates were reduced to the corresponding mendelic esters with 90percent, 96percent and 100percent ee, respectively.The reduction of the β-keto esters, however, proceeded slowly and ethyl acetoacetate gave the corresponding alcohol with 55percent ee.
Brown, Herbert C.,Pai, G. Ganesh
p. 1384 - 1394
(2007/10/02)

Remarkable Optical Induction in the Reduction of α-Keto Esters with B-(3-Pinanyl)-9-borabicyclononane. Synthesis of α-Hydroxy Esters of 100percent Optical Purity
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Brown, Herbert C.,Pai, Ganesh G.,Jadhav, Prabhakar K.
p. 1531 - 1533
(2007/10/02)